The field of the disclosure relates generally to seals for rotary machines, and, more particularly, to a centrifugally activatable seal for a rotary machine.
At least some known rotary machines, including, but not limited to, some known steam turbines, include a seal configured to prevent leakage of a working fluid through gaps between stationary and rotating components. At least some such known seals are configured to provide a clearance between the stationary and rotating components. For at least some such known seals, the clearance is selected to be sufficiently wide to reduce a breakaway torque required to start the rotary machine, and/or to limit an interference with axial movement of the rotating components relative to the stationary components. However, in at least some cases, increasing the width of the clearance to meet such requirements results in a corresponding increase in a residual leakage through the seal.
In one such rotating seal, a bristle pack is arranged so that when the rotating component rotates, the centrifugal force due to rotation pushes the bristles against a backing plate. Furthermore, the pressure differential across the seal also pushes the bristle pack against the backing plate. This makes the bristle pack significantly stiff. When the seal is stiff, it exerts larger normal load against the adjacent stationary component. With larger than normal loads, frictional force as well as rate of wear also increase.
Thus, it is highly desirable to provide a seal for a rotary machine that addresses one or more of the issues described above.